9.5.1 Policies when observing with G130M at LP7

In Cycle 33, G130M CENWAVE settings 1055, 1096, 1222, and 1291 will move from LP2, LP4, and LP5 to the new LP7, while CENWAVE settings 1300, 1309, 1318, and 1327 will remain at LP5.  Although the spectral resolution and sensitivity vary slightly with LP, these changes are mostly transparent to users. An exception is the use of LP7, which carries increased wavelength-calibration overheads due to the use of SPLIT wavecals.  To minimize the impact of these overheads, the following policy has been adopted for G130M observations for which the total exposure time is one orbit or less:

• Observers using G130M CENWAVE settings 1055, 1096, and 1222 or CENWAVE setting 1291 with detector SEGMENT=A are permitted to use fewer than four FP-POS based on the following S/N limits:
  • Users whose spectra require S/N > 25 are required to use 4 FP-POS.
  • Users whose spectra require S/N 20-25 are required to use at least 3 FP-POS.
  • Users whose spectra require S/N < 20 are permitted to use 2 FP-POS.
• Observers using G130M CENWAVE setting 1291 with detector SEGMENT=BOTH must use both of the available FP-POS.
• Observers using G130M CENWAVE settings 1300, 1309, 1318, and 1327 must use 4 FP-POS.

The savings in overhead from using fewer than four FP-POS must be balanced against the potential reduction in wavelength coverage.  See Section 13.3 for plots showing the wavelength coverage of each CENWAVE and FP-POS.

When calculating overheads for observations using G130M CENWAVE settings 1055, 1096, 1222, and 1291, be sure to account for SPLIT wavecal exposures.  Use Table 9.5 or APT to derive accurate overhead estimates.